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 * and open the template in the editor.
 */

package practice;


import java.math.BigInteger;
import java.io.IOException;
import static chanlib.Chan_Math.*;
import static chanlib.Chan_IO.*;
import static java.lang.Math.min;
import static java.lang.Math.max;

/**
 *
 * @author Chan
 */
public class FairWarning {
    /*
      All neccesary to be defined
      including:
      variable, inner class
    */
    // static int A;
    // static void B();
    // static class C


    /*
       One calculation fits all of the cases.
    */
    static void preReckon(){

    }

    /*
      calculate the answer
    */
    private static void reckon(int line) {
        int N=Int();
        BigInteger[] t=new BigInteger[N];
        for(int i=0;i<N;i++)
            t[i]=new BigInteger(String());
        int minI=N-1;
        BigInteger minT=t[N-1];
        for(int i=N-2;i>=0;i--){
            if(t[i].compareTo(minT)<0){
                minT=t[i];
                minI=i;
            }
        }
        BigInteger ZERO=BigInteger.ZERO;
        BigInteger GCD=ZERO;
        for(int i=0;i<N;i++){
            GCD=GCD.gcd(t[i].subtract(t[minI]));
        }
        BigInteger rem=t[minI].mod(GCD);
        BigInteger ans = rem.equals(ZERO)?ZERO:GCD.subtract(rem);
        String output=String.format("Case #%d: %s",line,ans.toString());
        writeln(output, OUTFILE);
        //writeln(String.format("N=%d K=%d\n%s", N, K, ans),ANALFILE);
        println(output);
    }


    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws IOException {
        /*
           Pre-computing for all cases
        */

        // Just in case!
        preReckon();
        //while((char)read()!='P');

        /*
          Input-output
        */
        boolean test=false;
        boolean small=false;
        String prob="B";
        String filename;
        if(test) filename="test";
        else{
            if(small) filename=prob+"-small-practice";
            else filename=prob+"-large-practice";
        }
        try {
            /*
               Init IO,plus determination of input line number
             */
            int lineNums = initFileIO(filename);
            for (int i = 1; i <= lineNums; i++) {
                reckon(i);
            }
        } finally {
            endIO();
        }
    }
}
